There is a recent trend of shifting the materials of fire extinguisher and LPG containers which have been made only from metals to resins due to deregulation in Japan. As compared with metal containers, resin containers have advantages that they are lightweight and easy to carry, rarely erode and have excellent designability.
Oxygen, nitrogen and CNG cylinders which require high pressure resistance as containers need such physical properties that they hardly embrittle at a low temperature since the reduction of temperature occurs due to the sudden release of internal pressure when a gas in the cylinders is discharged and used. Further, when a gas is stored in a container in a liquid state, such physical properties that the container hardly embrittles at a lower temperature range are required. Therefore, the modification of the physical properties of a thermoplastic resin which more easily embrittles at a low temperature range than metals is essential in order to use the thermoplastic resin in pressure-resistant containers and liquid gas storage containers. Aromatic polyesters typified by polyethylene terephthalate and polyethylene naphthalate have high strength, transparency, chemical resistance, heat resistance and gas barrier property at the time of stretching and therefore are used in various containers. However, since the aromatic polyesters embrittle at a low temperature range, it is difficult to use them in the above pressure-resistant containers and liquid gas storage containers.
JP-A 63-238155 discloses a composition comprising polyethylene naphthalate and a polyester elastomer. However, the glass transition temperature of the polyester elastomer is about −40° C. and has a problem that it cannot achieve sufficiently high impact resistance at a temperature range below −40° C. JP-A 2008-545018 discloses a composition comprising a thermoplastic resin and an ethylene-α-olefin copolymer. The ethylene-α-olefin copolymer has a glass transition temperature of −60° C. or lower and has an advantage that it has excellent impact resistance at a low temperature range. However, the ethylene-α-olefin copolymer has low compatibility with a thermoplastic resin having a carboxyl group at part of the end, typified by a polyester and therefore, the composition comprising the ethylene-α-olefin copolymer and the thermoplastic resin has such problems that it cannot achieve sufficiently high impact resistance and causes delamination when it is stretch-blow molded. JP-A 2011-256276 teaches that an ethylene-propylene-butadiene copolymer component and an ethylene glycidyl methacrylate copolymer component may be used in combination with a resin component containing an aromatic polyester. Since the ethylene glycidyl methacrylate copolymer serves as a compatibilizing agent, it is effective in preventing delamination at the time of stretch-blow molding but deteriorates low-temperature impact resistance since it has a methacrylate unit as a hard component.